NLA Editor, only top track is working
This is a little dated, but for anybody having this issue in the future, I finally found out how to fix this issue..

I have been trying to use the NLA Editor as a generic timeline to construct my animation, so I have a huge amount of actions and an endless amount of tracks in the NLA Editor. I finally found that in order to get each track to play simultaneously (sp?) no matter it's track position, you need to 

1) Hop over to the "Active Strip" options (Press N, then go to the "Active Strip" area

2) In the "Extra" dropdown menu, select "Nothing"

3) In the "Blend" dropdown menu, select "Combine"

That's it! Just make sure to do this with each action strip and everything will work good.... Note: You have to select the Action Strip itself, not the Track